A microscopic roughness structure having a microscopically rough structure on the surface in which fine concavities and convexities is regularly disposed, is known to exhibit antireflective performance by continuously changing the refractive index. In order for the microscopic roughness structure to exhibit satisfactory antireflective performance, it is required that the interval (period) between adjoining convexities or adjoining concavities be less than or equal to the wavelength of visible light. Such a microscopic roughness structure is also capable of exhibiting super water-repellent performance by means of the lotus effect.
Regarding the method for forming a microscopically rough structure, for example, those methods described below have been suggested.                Method of performing injection molding or press molding using a mold in which a microscopically rough structure is formed on the surface (Method 1).        Method of disposing an active energy ray-curable resin composition (hereinafter, described as a resin composition) between a mold and a transparent base material, curing the resin composition by irradiation of active energy radiation, thereby transferring the microscopically rough structure of the mold onto the cured product, and then detaching the mold from the cured product (Method 2).        Method of transferring the microscopically rough structure of a mold to a resin composition, subsequently detaching the mold from the resin composition, and curing the resin composition by irradiation of active energy radiation (Method 3).        
Among these, when the transferability of the microscopically rough structure and the degree of freedom of the surface composition are considered, methods of curing a resin composition by irradiation of active energy radiation, and transferring the microscopically rough structure of a mold (Methods 2 and 3) are suitable. These methods are methods that are particularly suitable in the case of using a belt-shaped mold or a roll-shaped mold, both which are capable of continuous production, and have excellent productivity.
However, a microscopic roughness structure has problems such as described below.                The microscopic roughness structure may have inferior scratch resistance compared with a molded product produced using the same resin composition and having a smooth surface.        When a film-like microscopic roughness structure having the microscopically rough structure of a mold transferred thereon is continuously produced, and this is wound into a roll form, if the hardness of the cured product is not sufficient, the shape of the microscopically rough structure (particularly the shape of convexities) may be changed by tight winding.        When a film-like microscopic roughness structure having the microscopically rough structure of a mold transferred thereon is attached to various displays and the like, the shape of the microscopic roughness structure (particularly the shape of convexities) may be changed by the load.        
Thus, for the purpose of maintaining (protecting) the shape of the microscopic roughness structure, there are occasions in which a protective film is affixed to the surface on the microscopically rough structure side until the microscopic roughness structure is used.
However, when the period of the microscopically rough structure is several nanometers (nm) to several hundred nanometers (nm), since the interval between convexities is narrower compared to conventional microscopically rough structures, the contact area between the microscopic roughness structure and the protective film is small.
Furthermore, it is difficult for the adhesive component of the adhesive layer of the protective film to penetrate into the concavities of the microscopically rough structure. Therefore, there are occasions in which the protective film does not sufficiently adhere to the microscopic roughness structure, and at the time of storage or transport, the protective film may be detached.
Regarding a protective film for an optical film having a microscopically rough structure on the surface, products described below have been disclosed.
(1) A protective film having an adhesive layer, for which when the adhesive layer is attached on a prism sheet, and then the prism sheet is pressed under particular conditions, the degree of penetration relative to the thickness of the adhesive layer of the prism sheet is 45% or less (Patent Document 1).
(2) A protective film having an adhesive layer having a surface roughness of 0.030 μm or less (Patent Document 2).
As such, a protective film is required to have close adhesiveness, and on the other hand, when a protective film including an adhesive layer containing an adhesive with stronger adhesive force than the conventional cases (strong adhesive protective film) is used, there is a problem that surface contamination of the microscopic roughness structure due to the adhesive occurs. This is speculated to be caused by the adhesive component of the adhesive layer penetrating deeply into the concavities of the microscopically rough structure as time passes, or by the adhesive component remaining on the surface of the microscopic roughness structure when the protective film is detached (hereinafter, these will be described as adhesive residue). Surface contamination of the microscopic roughness structure is led to a decrease in the antireflective performance. Specifically, the wavelength-dependency of reflectance may change, or the reflectance may generally increase.
Thus, regarding a protective film which can be easily affixed to a microscopic roughness structure and in which the adhesive component cannot easily penetrate deeply into the concavities of the microscopically rough structure, products such as described below have been disclosed.
(3) A protective film having an adhesive layer laminated on the surface of a base material film such that the protective film would be affixed to areas other than the microscopically rough structure of the microscopic roughness structure (Patent Document 3).
However, the protective films of items (1) to (3) do not necessarily sufficiently satisfy adhesiveness and the suppression of adhesive residue.